Flexible shaft couplings



April 18, 1961 P. c. HUNGERFORD, JR 2,979,925

` FLEXIBLE SHAFT CGUPLINGS Filed April 30, 1959 vnd D mm. m; N

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N r Hu A C. Pw

HSNSMSHSEMN 2,979,925 FLEXIBLE SHAFT coUPLnms Filed Apr. 3o, 1959, ser.No. 810,123

4 claims. (ci. 641s) This invention relates to flexible or universaltype couplings for shafts or generally aligned rotary elements, whereinone of the shafts or members to be coupled is adapted to be supported bythe other in centered relationship therewith at the axial center of thecoupling while permitting one of the two shafts or members to move outof alignment with the other remotely of such center to a limited extentduring operation to transmit torque.

Shaft couplings of the universal type utilizing helical springencircling relatively adjacent external drum portion of the shafts orcoacting with internal drum members attached to such shafts are wellknown. In all instances, so far as I know, the helical springs areemployed principally for the purpose of enabling torsional yield oflimited extent or in other words some relative angular movement of theshafts about their axes in the normal direction of operation to transmittorque. Such prior uni versal type couplings employing helical springsare incapable of accurately centering one shaft in reference to thecooperating shaft (piloting action), or, in other words, are incapableof serving as a satisfactory radial support vat all times for suchcooperating shaft. Usually the helical spring or springs involved insuch known couplings are normally spaced radially from the shaft endportions or equivalent drum members rigid with the shafts to be couple,and the angular yielding referred to nited States Patent O is limited bycontraction or expansion of the springs against the adjacent surfaces ofthe shafts or drum members carried thereby so that the couplings soformed are not positive or torsionally stiff. Plural springs (interwoundor intertwined) are also known in the art relating to universal typecouplings, but so far as I know none of the prior arrangements utilizingsuch interwound springs constitute an accurate means for holding theadjacent ends of the shafts in centered relationship While enablingmovement of portions of the shafts remotely of rice Additionally thepresent coupling allows strongly and uniformly resisted or controlledangular movement of the shafts about their axes in one direction only(torque limiting action) while operating as a torsionally rigid orpositive torque coupling in the opposite direction.

Because the present coupling operates as a very satisfactory pilotbearing or journal for one of each of two relatively adjacent shaftsconnected thereby, the problem of obtaining satisfactorily operatingalignment of three or more bearings, as in installations requiring twoor more long shaft sections with non-binding but laterally fixed rigidsupports, is greatly simplified.

Objects and features of the present invention not referred to orindicated above will be made apparent in the following description inreference to the accompanying drawing showing presently preferred forms.The essential characteristics are summarized in the claims.

In the drawing:

Fig. 1 is a diagrammatic assembly view showing two shafts connected bythe present coupling yunit or assembly in one form. k I

Fig. 2 is asimilar diagram showing two shafts with a conventionaluniversal type flexible coupling (shown in outline only) of such type aswill not positively center the shafts or support one from the other at apoint between the two shafts.

Fig. 3 is a relatively enlarged View of the present coupling partly inlongitudinal cross section and portions of two shafts as connected bythe coupling.

Fig. 4 is a transverse sectional view taken as at line 4-4 on Fig. 3.

Fig. 5 is a partly elevational and partly cross sectional view showing amodified form of the present coupling and a portion of a hollow shaftespecially adapted to be made of light weight metal.

Fig. 6 is a fragmentary view of a modified helical spring assembly foruse in the present coupling.

Fig. 7 is a fragmentary view generally similar to Figs. 3 and 5 showinga portion of a shaft and a portion of a modified spring assembly.

Referring to Fig. 1, shafts 1 and 2 are normally aligned at theiradjacent ends within the present helical vspring coupling unit assembly10. One of the shafts has a conventional arrangement of bearings A and Bso Vthat the end portion of the shaft 1 which projects within thecoupling assembly 10 has its principal support as a cantilever frombearing B. Shaft 2 requires a` bearing .C remotely of the couplingassembly 10 but requires no bearing adjacent the coupling.

In Fig. 2 wherein the shafts 1 and 2 are connected by a conventionalflexible or universal type coupling E the couplings out of alignment oras accomplished by more or less complex, transversely bulky andrelatively expensive universal joints or shaft-coupling mechanism.

The present coupling unit or mechanism which may .consist solely ofthree interwound helical springs of uni- .form diameter in interferenceor preloaded relationship to the shaft ends (or drums thereon) providesa torsionally stilf and radially approximately stiff universal typecoupling enabling the shaft axe's to be angularly movable out ofalignment while being maintained solidly and accurately centered or withtheir axes intersecting at the axial center of the coupling. Thus thepresent coupling vwhile being of relatively simple construction andradially extremely compact as compared to most universal type couplings,operates essentially as does a so-called Thomas type coupling having aexible metal disc and two pairs of coupling pins parallel to respectiveshaft axes and attached solidly to the respective shafts tobe'conn'ected and arranged snugly to venter mating holes in the disc,the two pairs of holes and pins being at right angles to which has noshaft aligning or piloting action or capabili` ty the bearings A', B andC must be augmentedby an additional radial bearing D'. If a shaft suchas 2 of Fig. 1 were to be disposed intermediately of two shafts (notshown) each having bearings such as A and B, then such (non-illustrated)shaft Z would not require any bearing C, assuming a present couplingunit 10 were to be provided at each end of such intermediate shaft 2.

In Fig. 1 the three helical springs 5, 6 and 7 are adapted to be heldinposition against moving along the shafts 1 and 2 in either longitudinaldirection by means of short radial toe portions (not shown) of thesprings located at the left end of the spring assembly 10 and looselyoccupying a shallow peripheral groove 1a in shaft 1. lThe spring toesare sprung into place in the groove.' In Fig. 3 the helical springassembly 10 is positioned axially by collars 11 and 14 suitably securedto the respective shafts 1 and 2 as by pins 12 or other suitablefastening y spaanse of coupling assembly 1Q' are spacedapart as at .3(crossover region) a suitable distance depending upon the amount oftransverse misalignment that can be expected in service incident torequirement of lateral movement of one end of the shaft 2 -opposi-te'its .illustrated end (eg. as would be the case in a ypropellershaft of`an Vautomotive vehicle). The spacing at crossover 3, .as will be morefully explained below, is not particularly critical as to dimensions,o-r in other words may vary over wide limits, thus, inter alia,facilitating assembly with whatever frame or cooperating mechanism`components (not shown) are involved.

The adjacent ends of shafts V1 and 2 Vhave suitable drum-constituting orapproximately circula-r surfaces 1a and 2a enveloped by the individualspring :members 5., 6 and 7 and extending to the crossover region 3. Thethree spring members 5, 6 and 7 are preferably `.made by open winding(e.g. with a triple thread e'iectras compared to screw threads) withapproximately or Anearly `twice .the distance between individual turnsvas the width or thickness of the coiled spring stock measured axiallyof thc coupling assembly 10'. Then the three springs are screwedtogether or interwound 'for example as shown by patent of W. C. Starkey,1,966,267, dated July l0, 1935, relating to a spring clutch (not laflexible or universal type coupling).

The three springs 5, 6 and 7 may be held circumferentially in positionat one end of the coupling or coupling assembly 10', so as to preventrelative Vangular movement of the springs about their longitudinal axis,as by above Ymentioned collar 11. One way of holding the ends of thespring members in 120 angularly spaced apart relationship or as shown inFig. 3 is to provide axial sockets or holes 13 adapted to receiveparallel toe or bent out lug portions 6' and 7 of the individual springmembers. 1f desired the end portions of the springs associated with thecollar 11 maybe tightly joined to the collar 11 as by welding, brazingor pinning V(not illustrated). -In that c'ase, since in operation thespring assembly 10' could not crawl out of position along the shaft asin a direction from shaft 1 towards shaft 2, abutment or positioningmeans 14 for the opposite ends 5a, 6a, etc. of the springs would beunnecessary. If the individual spring members are not fastened together(e.g. as assumed and partially shown in Fig. 1) and are not restrainedfrom circumferential movement relative to shafts 1 and 2 (as in Fig. 1)then coils at both ends of the spring assembly can (to advantage asalready indicated) overrun on the associated shaft portions. When lugs5', 6 etc. are provided as shown in Fig. 3 then, during overrun, thelugs are subiected to at least some strain and tiexure, particularly ifthe spring coils are heavily preloaded on the shafts.

It is important that at the crossover gap on region 3 and for so-medistance along each shaft `therefrom the spring coils shall bepermanently in interference fitting or preloaded relationship to theshaft or drum surfaces 1a and 2a. Usually in practice all the coils areuniformly preloaded against those surfaces. IReferring to Fig. 4 it willbe noted that the plane of the section cuts the three spring members 5,6 and 7 at regions exactly 120 apart from each other. Such 120relationship occurs'at all points intermediately of the end portions ofthe spring assembly, hence the three spring members in the region of thecrossover 3 have the capability of strongly holding the adjacent ends ofthe shafts exactly concentric with each other at point P, Fig. 3, whichis coincident with the common axis of the shaft end portions when and ifthe shafts are aligned. Notably, as exhibited by Fig. 3, the individualspring coils bridge the crossover gap 3 at roughly three times the angleat which a single or nor1nallygclose-coiled clutch spring formed of asingle helical member would bridge the crossover gap.l This has theadvantage of enabling use of a crossover gap 3 wider if desired or foundexpedient for assembly purposes as previously mentioned, than the widthof the spring coil stock 4 axially of the shaft without danger of thecoils .entering the gap or effective groove provided at the crossover.Thus the present coupling in all forms disclosed hereby can enableconsiderable angular displacement of one shaft with reference to theother about the axial center of the coupling.

In operation it will be apparent that the springs 5, 6 and 7 are selfenergizing at their free ends (eg. end portions 5a, 6a, etc.) hence gripthe shaft drum portions 1a and 2a with exponential force increase aswell known in spring clutch practice toward the crossover region 3. Thecoil assembly or coupling 10' is absolutely stiff torsionally in thedirection of operation indicated by the arrow at the left in Fig. 3.Since the free end portions 5a, 6a and 7a are not attached to the shaft2 and can have any desired preloading against drum surface 2a within thelimits of elasticity of the spring stock, considerable torque can betransmitted in the reverse direction or opposite of the arrow in Fig. 3before overrun of the coils on drum surface 2a occurs. The torquecapacity of the present exible coupling unit in the normal direction ofoperation is determined, as in spring clutches, by the material andcross section of the spring stock and the number of coils of eachindividual spring member 5, 6, 7 (or more) which operate in parallelwith each other. Similarly in operation in the torque limiting direction(opposite of arrow) the torque capacity of the coupling unit is the sumofthe overrunning torque values for which the individual spring membersare designed, and the friction 'drag (during overrun) lis essentiallyconstant under all conditions despite variations in coeicient offriction, which may vary widely.

Fig. 5 shows uniformly circumferentially spaced free terminal portions5", 6" and 7-' of the three spring coil members 5, 6 and 7 in positionfor abutment with collar 11' or an axial shoulder (not shown) formed onthe shaft 1. At the opposite end of the spring` assembly 10" the axialpositioning means 14' is shown as an axial shoulder formed on the shaft2", and the associated spring coils are preloaded on the thereby reduceddiameter end portion of the shaft. Shaft 2, as shown, is hollow and if,additionally to minimize its mass, the shaft is made of a light weightmetal such as aluminum then the end of such shaft which terminateswithin the coil spring assembly 10 may be reinforced as necessaryadjacent the crossover lregion 3 where the maximum gripping forces ofthe coilsor the coupling occur. The reinforce may be in the form of ahard metal plug (e.g. tightly fitting into the hollow end of the shaft)or may comprise a cap such as illustrated at 15 secured as by screws 16.In event of using such relatively soft material for one or both of theshafts, then each shaft so composed would have such reinforce means 15or the like as described above. In an arrangement such as Fig. 5 (orFig. l) the coil members 5, 6 and 7 are operatingly secured to both theshafts 1 and 2" solely by interference fitting between the coil membersand associated shaft surfaces.

Fig. 6 shows the three coil members 5, 6 and 7 with co-planar terminalportions at one end of the coil assembly 103, providing acircumferential flat shoulder or abutment 17. In this case a ring orcollar similar to part 11, Fig. 3, could be used if desired (notillustrated) having a helix formation of known form for receiving theend portions of the three springs or, alternatively, the ring or collarsuch as 11 in Fig. 5 could merely abut the axially outermost end portionof the coil member 5 as a travellimiting stop. The three end portions ofthe coil assembly 103 of Fig. 6 (or in any case for that matter) can bebrazed together or otherwise fixed to each other against relativeangular movement about the common longitudinal axis of the springs as atregions indicated 18 and 19 in Fig. 6.

Obviously the drum surface portions 1a and 2a of shafts` 1 and 2 couldbe internal instead of external or the drum surface on one shaft couldbe internal and the operationally corresponding drum surface on theother shaft could be external.

Fig. 7 is a fragmentary view generally similar to Figs. 3 and 5, furthershowing the coupling construction aocording to Fig. 1 but with theaddition of a positioning member 18 similar to a snap ring looselyseated in the groove 1b of shaft 1 in the transverse plane of thenwardly bent toe portions 5b, 6b and 7b of the three helical springmembers to hold the toe portions just mentioned in 120 spacedrelationship around the groove in the shaft. The two free ends of thepositioning `member provide shoulders (one indicated 19 in Fig. 7) tolocate or position one toe portion (e.g. 6b) and has inwardly facingnotches (not shown) formed therein to embrace the other two toe portions5b and 7b.

I claim:

l. In combination with two rotary shafts axially spaced v apart at theiradjacent end portions, a exible coupling for said adjacent end portionsand comprising a coil assembly having at least three interwound helicalspring members preloaded in interference fitting relationship tocircular peripheral surfaces of both shaft end portions,v

the individual spring members being attached to each other so as toprevent relative angular movement about the longitudinal axis of thespring members.

2. The combination according to claim 1, wherein one of the shafts isgenerally composed of light weight metal such as aluminum and its endportion within the spring assembly is peripherally reinforced adjacentthe axial space or cross over region between the two shafts.

3. A universal joint coupling enabling angular exibility betweenrotatable shafts having axially spaced apart drum surface portions ofcircular cross section and of approximately equal diameters, a coilassembly com-r prising at least three interwound elastic metal helicalcoil members bridging and preloaded against the drum surface portions ofboth shafts and operating strongly t0 hold their adjacent end portionssubstantially in alignment while inexibly transmitting high torque fromone to the other in one direction, the preloaded coilmembers beingsecured to one of the shafts solely by such preloading whereby to enableoverrun on the drum surface of one shaft in the opposite direction,While effecting transmission of substantial torque to or through thatshaft in said opposite direction and means positively securing the coilmembers to each other against angular relative movement of the membersabout the axes of the shafts.

4. In combination with two rotary shafts axially spaced apart at theiradjacent end portions, a ilexible coupling for said adjacent endportions and comprising a coil assembly having at least three interwoundhelical spring members preloaded in interference fitting relationship tocircular peripheral surfaces of both shaft end portions, the springassembly being held in position axially by radially extending toeportions of each of the individual spring members projecting into aperipheral groove in one of the shafts, and a member occupying thegroove, turnable therein, and having circumferentially spaced shouldersengaging end portions of the springs to prevent the splilings frommoving out of angular relationship to each ot er.

References Cited in the le of this patent UNITED STATES PATENTS

